Rate reducer

ABSTRACT

An automatic firearm incorporates an integral rate reduction device which delays hammer fall. The rate reduction device is associated with an automatic sear and includes an inertia mass adapted to be pivoted by the hammer during initial hammer fall. In semiautomatic operation, the inertia mass is not displaced by the hammer when it is pivoted between a cocked position and the fired position, since all rate reducer action is completed before a shooter pulls the trigger.

11] 3,724,325 Apr. 3, 1973 nited States Patent {191 Silsby 2 459 1581/1949 Garand...................................89/l3l 2,215,470 9/1940Johnson [54] RATE REDUCER [75] Inventor: Stanley D. Silsby, Granby,Mass.

[73] Assignee: Colts Industries Operating Corp., P i E i er-Stephen C.Bentley fi York, NY Attorney-Radford W. Luther ABSTRACT An automaticfirearm incorporates an integral rate reduction device which delayshammer fall. The rate N .mL

[52] US. Cl......,..................89/l31, 42/1 S, 42/75 C, reductiondevice is associated with an automatic sear 1m Cl 89/142 a g andincludes an inertia mass adapted to be pivoted by 89/129, 131,149,154the hammer during llll la hammer a In semrauto [58] Field ofSearch........

matic operation, the inertia mass is not displaced by the hammer when itis pivoted between a cocked posi- [56] References C'ted tion and thefired position, since all rate reducer ac- UNITED STATES PATENTS tion iscompleted before a shooter pulls the trigger.

3,129,637 4/1964 Packard 9 Claims, 11 Drawing Figures PATENTEUAPRS I9753.724;.325

SHEU 1 BF 4 PATENTEDAPRB I975 SHEET 2 [1F 4 PATENTEUAPR3 I975 SHEET 30H1 RATE REDUCER BACKGROUND OF THE INVENTION The invention relates toautomatic firearms and more particularly to automatic firearms whichincorporate a means to reduce the rate of fire in automatic operation.

Arrangements which serve to reduce the rate of fire during automaticoperation are known in the prior art. An example of such a mechanism isshown in U.S. Pat. No. 3,30l,133 issued to F. E. Sturtevant. While themechanism as shown in this patent yields eminently satisfactoryoperation, it occupies space in an area which does not exist in allweapons.

SUMMARY OF THE INVENTION The invention contemplates the use of a ratereduction device which incorporates a pivotally mounted inertia mass.Cooperating means on the hammer and the mass act to rotate the inertiamass during initial hammer fall, thereby delaying hammer fall duringautomatic operation. An automatic sear engages the inertia mass toprevent its displacement by the hammer until the bolt is completelylocked. This arrangement effectively reduces the rate of fire to anacceptable value and does not require excessive space in the receiver ofthe firearm. Moreover, a rate reducer according to the inventionrequires a minimum number of components.

Accordingly, it is a primary object of the invention to provide afirearm including means capable of automatically retarding the rate offire or speed at which the firearm is discharged during automaticoperation.

Another object of the invention is to provide an automatic firearmpossessing a delayed automatic firing feature which does not necessitatethe provision of excessive space in the receiver.

A further object of the invention is to provide a firearm including arate of fire reducer for automatic operation which is associated with anautomatic sear.

A still further object of the invention is to provide a firearm having arate reducer for automatic operation which does not impair the accuracyof the firearm during semiautomatic operation.

Other objects and advantages of the invention will become apparent ofthe following detailed description taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an isometric view of afirearm incorporating a rate reducer according to the invention.

FIG. -2 is an isometric cutaway view of the firearm of DETAILEDDESCRIPTION OF PREFERRED EMBODIMENT turning now to the drawings indetail, there is shown in FIG. 1 an automatic, gas-operated firearm 12.The

firearm 12 includes a receiver section generally shown at 14 having anupper receiver 14a and a lower receiver 14b. A magazine 16 is partiallycontained within the receiver section 14 for delivering cartridgesthereto. Connected to the upper receiver is a barrel 18. A trigger 22 isdisposed forwardly of a hand grip 24. The trigger 22 is mounted upon thebarrel 18 for axial movement parallel to the axis of the barrel androtational movement thereabout. Secured above the barrel 18 is a gastube 26 which contains the piston for successively cycling the operatingcomponents and cocking the firing mechanism during automatic andsemiautomatic operation. At the front and rear ends of the firearm arerespectively located sight assemblies 28 and 30. The three post sights,which constitute the front assembly, are threadably secured to thefirearm in front of the tube 26 for vertical adjustment to obtain theproper elevation when zeroing in the firearm. The rear sight 30comprises three peeps, each adapted to be used with a corresponding poston the front sight as sembly 28 in accordance with the selected pistolgrip position.

Turning now to FIG. 2, the construction of the firearm 12 may be betterappreciated. As shown in FIG. 2, the barrel 18 comprises a chamber 32adapted to receive a cartridge inserted therein by a bolt assembly 33.When a cartridge chambered in chamber 32 is fired during eitherautomatic or semiautomatic operation, the bullet travels outward throughthe bore of the barrel 18 under the impetus of the expanding gases. Someof these gases are diverted through the gas port 36, formed in thebarrel 18 into a chamber 38, defined by the gas tube 26 and a piston 39attached to the forward end of an operating rod 40, the rod 40 beingdisposed within the tube 26 for axial movement therein. Secured to thebarrel 18 is a spring stop 42 which serves as a spring seat for anoperating spring 44 which is coiled around the operating rod 40. Hence,the gas pressure generated within the chamber 38 by the expanding gasesdrives the operating rod 40 rearwardly, against the bias of theoperating spring 44, to cycle the operating components and the firingmechanism in a manner explained hereinafter. A depending abutment 48,carried by the operating rod 40, engages the bolt carrier 50 of the boltassembly 33 so as to impart reciprocating movement thereto within theupper receiver 14a. The operating rod 40 is also provided with acharging handle 52 to manually charge the weapon and an ejection opening54 through which spent cases are ejected. In order to expose thecomponents of the firing mechanism for cleaning, maintenance or otherpurposes, the lower receiver 14b is mounted upon a pivot pin 56 and takedown pin 58.

Before a detailed discussion of the firing mechanism incorporated in thelower receiver 14b, it would be profitable to briefly examine thestructure of the bolt assembly 33. The bolt assembly 33, which ismounted for longitudinal reciprocating movement between retracted andbattery positions within the upper receiver 14a, is of a type known inthe prior art. The bolt carrier 50 of the bolt assembly 33 moveslongitudinally with the receiver under the impetus of the operating rod40. The guide lugs 60 and 62, defined on the upper part of the boltcarrier 50, function to prevent rotation of the bolt carrier 50 duringlongitudinal movements. Mounted for axial sliding movement and rotationwithin the bolt carrier 50 is a bolt 64 having a plurality of lockinglugs 66 fashioned upon the front end thereof, the locking lugs 66 beingadapted to pass through and lockingly engage a corresponding set of lugs68 defined in the upper receiver 14a adjacent chamber 32. When the bolt64 moves toward the chamber 32 to its battery position, the locking lugs66 pass through the voids between the corresponding lugs 68 and thenrotate to positions in which they lockingly engage the lugs 68 inaccordance with the rotation of the bolt 64. The locking cooperationbetween the lugs 66 and 68 holds the bolt 64 in the illustrated batteryposition to lock the bolt 64 against rearward movement, as is urged whena chambered cartridge is fired.

The bolt assembly 33 also includes a firing pin 70, slideably mountedwithin the bolt 64 and the bolt carrier 50 for restricted reciprocatingaxial movement. As best seen in FIGS. 2, and 6, a cam pin 72 extendsthrough a bore in the bolt 64 and embodies an aperture which slidinglyreceives the firing pin 70. The cam pin 72 travels within a helical camslot 74 in the bolt carrier 50 which is disposed between the guide lugs62 and 60. When relative longitudinal movement is occasioned between thebolt carrier 50 and the bolt 64, the cam pin 72 produces relativerotation between the bolt 64 and the bolt carrier 50, the guide lugs 60and 62 restraining the bolt carrier 50 against rotation. The firing pin70 is restricted in its longitudinal movement with respect to the boltcarrier 50 and the bolt 64 by virtue of a pin 76 fixably secured to thebolt carrier 50 and extending within an aperture 78 in the rear of thefiring pin 70. This restricted movement of the firing pin 70 withrespect to the bolt carrier 50 and the bolt 64 prevents a chamberedcartridge from being fired before the bolt 64 is locked. Hence, if forany reason the firing pin 70 should be struck when the bolt 64 is notlocked, the chambered cartridge will not be fired.

For the purposes of illustrating the operation of the bolt assembly 33,assume that a cartridge has been fired and that the bolt assembly 33 istraveling in a rearward direction toward the buffer 79 its retractedposition. Since the bolt 64 is locked by the engagement between thecooperating lugs 66 and 68, rearward movement of the bolt carrier 50will produce rotation of the cam pin 72 and hencerotation of the bolt64. This rotation of the bolt 64 causes the locking lugs 66 to confrontand register with the voids defined between the cooperating lugs 68 toallow rearward movement of the bolt 64 upon further movement of the boltcarrier 50. The driving force is transmitted to the bolt 64 via the campin 72 by the front surface of cam slot 74. During rearward movement orrecoil of the bolt assembly 33, the expended cartridge is extracted andejected. The dissipation of the rearward momentum of the bolt assembly33 and operating rod 40 is primarily attributable to the operatingspring 44 which is adapted, at the termination of recoil upon contactwith the buffer 79, to urge the operating rod 40, and hence the boltassembly 33, toward the battery position thereof. During forwardmovement of the bolt assembly 33, a new cartridge is stripped from themagazine 16 by bolt 64 and chambered.

The heart of the invention resides in a rate reducer which isincorporated in the firing mechanism mounted in the lower receiver 14b.In order to appreciate the construction of the firing mechanism, it isuseful to refer to FIG. 2 in conjunction with FIGS. 3 and 4. Beforecontinuing the discussion of the firing mechanism, it is important tonote that the selector 80 is set for automatic fire and that themechanism is cocked and ready to fire.

A hammer 82 is mounted on a pivot pin 83 for swinging movement between arecoil position and a fired position, the illustrated cocked position(FIGS. 2 and 3) being intermediate these extreme positions. A torsionspring 84 is coiled around the hub 86 of the hammer 82 to bias thehammer 82 toward the fired position. The hammer 82 includes a searingsurface 88, which is engageable by the sear 90, and a notch 92,engagable by a leg 94 of a disconnect 96 during semiautomatic operation.The upper portion of the hammer 82 comprises a recess 98 in which a link1100 is mounted for pivoting movement about a pivot pin 102. The link100 is urged in a counterclockwise direction about pivot pin 162 by aspring and plunger assembly 104 such that the protrusion 106 of the link100 projects from the outer contour of the hammer 82, the function ofthe protrusion 106 being explained hereinafter. Turning back to the sear90 and the disconnect 96, it can be observed that both the sear 9t) andthe disconnect 96 are mounted about a common pivot pin 108 an are biasedin respective clockwise and counterclockwise directions by a compressionspring 1 10 positioned therebetween.

The selector 80 is mounted upon a pin 118, fixedly secured in the lowerreceiver, to limit the movement of the sear 90 and disconnect 96 suchthat the firearm 12 may be rendered safe or adapted for semiautomatic orfully automatic operation, in accordance with the position of theselector 80. Briefly stated, when the selector 80 is moved to safe, thesear 90 is contacted such that movement of the trigger 22 cannotdisplace it out of engagement with hammer searing surface 88. In thesemiautomatic position of the selector 80, the selector 80 is positionedsuch that the disconnect 96 may rotate under the influence of thecompression spring 1 10 so as to position the leg 94 thereof under thenotch 92 of hammer 82, thereby preventing clockwise rotation of thehammer 82. In the automatic position of the selector, which is thatillustrated in FIGS. 2 and 3, the disconnect 96 is displaced clockwiseabout the pin 108 such that the leg 94 will not engage the notch 92 whenthe hammer moves towards the fired position from the recoil position.

As shown in FIG. 6, during recoil, the bolt assembly 33 drives thehammer 82 downwardly or counterclockwise about pivot pin 83. When thehammer 82 reaches its lower or counterclockwise limit of travel(referred to herein as the recoil position), the end of hammer 82impacts upon a resilient buffer 122 which serves to cushion the loadsimparted to the hammer 82 by the sudden stoppage of movement, thisposition being below or counterclockwise of the cocked positionindicated in Flg. 3.

As best shown in FIGS. 2 and 5-10, a trigger rod 124 interconnects thesear 90 and the trigger 22. The sear 90, itself, comprises an upstandingarm portion 126 which is adapted to be pushed by the trigger rod 124 soas to rotate the sear 96 to thereby releasethe hammer 82 for fallingmovement. Thus, by virtue of the interconnection (not shown) between thetrigger rod 124 and the trigger 22, rearward displacement of the trigger22 causes rotation of the sear 90 such that the hammer 82 is disengagedtherefrom.

A rate reducer mechanism is constituted by an inertia mass 134 and anautomatic sear 136 in the form of a bar. The inertia mass 134 is mountedfor pivoting movement between seated and displaced positions about a pin137 and is biased to the seated position, as illustrated in FIG. 3,wherein the rear surface of the inertia mass abuts a buffer 138. Thisbiasing is accomplished by a torsion spring 140, coiled about the hub ofthe inertia mass 134 and in contact with a fixed pin 142 located on theright side of the receiver, as is best shown in FIG. 4. The upper partof the inertia mass 134 adjacent the pivot pin 137 comprises contactsurface 146 and a searing surface 148. The contact surface 146 isadapted to engage the protrusion 106 of link 100 upon falling of thehammer 82 from its recoil position so that the spring bias acting on thehammer 82 must overcome the inertia of the inertia mass 134 and the biasimposed thereupon by spring 140 in order to displace the inertia mass134. Hence, since the hammer 82 must overcome the inertia of the inertiamass 134 and the bias of the torsion spring 140 to an extent sufficientto cause the protrusion 106 of link 100 to clear the contact surface146, the time for the hammer 82 to fall from its recoil position to thefired position will be extended from that of a free falling hammer.

Obviously, it is necessary to provide an automatic sear device to delayhammer fall until the bolt 64 is locked. This function is achieved, inaccordance with the invention, by the automatic sear 136 acting inconcert with the inertia mass 134. The searing surface 148, fashioned onthe hub of the inertia mass 134, is engaged by the surface 136a ofautomatic sear 136 to prevent the hammer 82 from rotatably displacingthe inertia mass 134 until the bolt 64 is locked and the bolt carrier 50is substantially in its battery position. To this end, the automaticsear 136 is biased toward the rear of the firearm 12 by a compressionspring 136b disposed in the upper receiver 14a adjacent the chamber 32,as best shown in FiG. 5. When the bolt carrier 50 is initially,rearwardly displaced from its battery position, spring 136k acts to movethe axially movable automatic sear 136 within its channel to the rearuntil a projection 136:: contacts an abutment pin 150, fixedly mountedin the upper receiver 14a. When this contact is established, the surface136a of the automatic sear 136 will overlie the searing surface 148 ofthe inertia mass 134 such that the urging of the hammer 82 upon thesurface 146 will not effect rotation of the inertia mass 134 so that thehammer 82 will be thereby prevented from moving to strike the firing pin70. However, as the bolt carrier 50 assumes its battery position, anabutment 152, fashioned on the bolt carrier 50, contacts anotherprojection 154 on the forward portion of the automatic sear 136 toaxially move the automatic sear 136 toward the chamber 32, thereby toremove the surface 1360 from restraining contact with searing surface148 of inertia mass 134. When the surface 136a of automatic sear 136slides out of contact with the searing surface 148 of the inertia mass134, the hammer 32 is then capable of rotating the inertia mass 134 inits falling movement toward the fired position.

OPERATION A. Automatic Operation With the firing mechanism in the cookedor seared configuration of FIG. 3 and the selector set for automaticfire, it should be apparent that depression of the trigger 22 will causedisengagement of the sear W) from the hammer searing surface 88, therebyallowing the hammer 82 to pivot under the bias of torsion spring 84 andeventually strike the firing pin 70 (FIG. 5). The striking of the firingpin 70 by the hammer 82 causes the bullet of the chambered cartridge topass outward through the barrel 18 under the propelling force of theexpanding gases. As previously described, a portion of these gasesenters gas port 36 and drives operating rod 40 rearwardly. The rearwardmotion of the operating rod 40 is imparted to the bolt carrier 50 in amanner heretofore described.

The initial rearward movement of the operating rod 40 is depicted inFIG. 6, wherein the bolt carrier 50 has not yet moved to such an extentto cause the locking lugs 66 on the bolt 64 thereon to be completelyrotated out of locking engagement with the corresponding lugs 68 on thereceiver. As FIG. 6 shows, the motion imparted to the bolt carrier 50 bythe operating rod 40 causes the end of the firing pin 70 to drive thehammer rearwardly or counterclockwise. It will be noted that in FIG. 6,the bolt carrier 51) has traveled a sufficient distance to the rear toremove the firing pin 70 from contact with the spent cartridge and toallow the automatic sear 136 to slide over the searing surface 148 ofthe inertia mass 134. In FIG. 6, the cam pin 72 is starting to rotate,thereby commencing rotation of the bolt 64 along with the integrallocking lugs 66.

Further movement of the bolt carrier 50 from the position shown in FIG.6 will cause sufficient rotation of the bolt 64 to enable the lockinglugs 66 to register with the voids between the corresponding lugs 68 onthe upper receiver 14a so that the end wall of the cam slot 74 willcontact the cam pin 72 and thereby produce rearward travel of the bolt64 to the position of FIG. 7. Movement of the bolt 64 from the positionof FIG. 6 to that of FIG. 7 also extracts the spent cartridge.

FIG. 7 shows that the bolt carrier 50 has moved the hammer 82 to aposition in which the link has been pivoted and depressed by the contactof protrusion 106 with the hub of the inertia mass 134. As can beobserved from FIG. 7, the slight rotation of the link 100 about its pin102 has slightly compressed the spring biased plunger 104. i

In FIG. 8, the bolt carrier 50 has produced a rearward rotation of thehammer 82 to its recoil position. Since the protrusion 106 on the link100 has cleared the hub of the inertia mass 134, the link 1110 occupiesits normal position. Also, in FIG. 8, the endof the hammer 32 is shownimpinging upon the buffer 122. The case is ejected when the bolt 64 isintermediate the FIGS. 7 and 8 positions. After the bolt carrier 50reaches its retracted position in which the buffer 79 is contacted, theforce of operating spring 44 acting on the operating rod 40 will urgethe bolt carrier 50 from the retracted position to the battery position.

The configuration shown in FIG. 9 depicts the cooperation between thehammer 82 and the inertia mass 134 when the bolt carrier 50 is movedforward of its retracted position, stripping a fresh cartridge from themagazine 16. As shown in FIG. 9, the protrusion 106 of link 1011 is inengagement with the contact surface 14-6 of inertia mass 134, therebycurtailing the fall of the hammer 82 to the fired position. Thisinterruption in the hammer fall is, of course, due to the movementpreventing engagement between the searing surface 148 of the inertiamass 134 and surface 136a of the automatic sear 136.

In FIG. 10, the fresh cartridge has been chambered by bolt 64 and thebolt carrier 50 is about to commence rotation of the cam pin 72 to lockthe bolt 64 in the battery position. It will be noted from FIG. 10 thatthe firing pin 70 is maintained at a safe distance from the cartridgeand that the automatic sear 136 continues to prevent displacement of theinertia mass 134 by hammer 82 and hence, the hammer 82 cannot yetcomplete its fall to the fired position.

As the bolt assembly 33 moves from the FIG. 11 to the FIG. 11 position(battery position), the bolt 64 is rotated and locked and, subsequentlythe abutment 152 in the bolt carrier 50 engages the projection 154 onthe automatic sear 136 to axially move the automatic sear 136 forwardagainst the bias of spring 136b. It should be noted that it is the lastportion of the forward movement of the bolt carrier 50 which results inthe surface 136a clearing the searing surface 148 of the inertia mass134 to thereby permit the inertia mass 134 to be rotated by theprotrusion 106 of link 1041. Also, this movement permits the firing pin70 to assume a position wherein it can contact a cartridge. The hammer82 will continue to rotate the inertia mass 134 until protrusion 106clears the contact surface 146, at which time the hammer 82 willcontinue its forward movement to the fired position and the inertia mass134 will return to its original or seated position (i.e., the positionillustrated in FIGS. 4 through 8), this repositioning being occasionedby the bias of the torsion spring 1410 acting on the inertia mass 134.

Hence, the fall of the hammer 82 to the fired position during automaticoperation is effectively delayed by the inertia of the inertia mass 134.After clearing the inertia mass 134, the hammer 82 falls to the firedposition, illustrated in FIG. 5, to fire another cartridge whichinitiates another cycle. It will be appreciated that the time consumedby displacement of the inertia mass 134 provides the desired reductionin the inherent rate of fire. To discontinue automatic firing, it ismerely necessary to release the trigger 22 so that the sear 90 willengage the hammer 82 during falling movement thereof.

B. semiautomatic Operation In general, with respect to semiautomaticoperation, the inertia mass 134 is displaced as in automatic operationexcept that the falling of the hammer 82 is interrupted by the contactbetween the disconnect 96 and the hammer 82. More particularly, if acartridge has been fired and the selector 80 occupies its semiautomaticposition, the hammer 82 will rotate the inertia mass 134, as previouslyillustrated and described, and after clearing the inertia mass 134, thenotch 92 will contact the leg 94 of the disconnect 96 to stop thefalling movement of the hammer 82. This assumes, of course, that theoperator of the firearm holds the trigger 22 in the depressed position.Upon releasing the trigger 22, both the disconnect 96 and the sear 90will be caused to rotate clockwise about the pivot pin 10% so that theleg 94% moves out of locking engagement with the hammer 82 and thehammer 82 subsequently rotates a few degrees and engages the sear 90. Itwill be appreciated that this is the case with many automatic firearms.The hammer 82 is now in cocked position and may be again fired bydepressing the trigger 22. It will be noted that the movement of thehammer 82 from the cocked to the fired position in semiautomaticoperation is in no way affected by the inertia mass 134.

Obviously, variations, modifications and adaptations of the heretoforedescribed structure are possible without departing from the spirit andscope of the invention as defined in the appended claims.

What is claimed is:

1. In a firearm adapted for semiautomatic and automatic operation, thecombination comprising:

a hammer mounted in the firearm for falling movement between recoil andfired positions;

a sear mounted in the firearm to engage the hammer and retain it in acocked position intermediate the recoil and fired positions; and

an inertia mass movably mounted in the firearm such that fallingmovement of the hammer from the recoil position to the cocked positioncauses the hammer to engage and displace the inertia mass and to clearthe inertia mass before reaching the cocked position in bothsemiautomatic and automatic operation and such that the hammer remainsclear of the inertia mass in falling movement from the cocked positionto the fired position in both semiautomatic and automatic operation.

2. The combination of claim 1, further including:

a bolt assembly mounted for reciprocating movement between retracted andbattery positions in the firearm, the bolt assembly being contacted bythe hammer in the fired position thereof; and

an automatic sear mounted in the firearm to engage the inertia mass suchthat displacement of the mass by the hammer is prevented, the automaticsear adapted to be contacted by the bolt assembly as it moves into thebattery position to remove the automatic sear from engagement with theinertia mass and thereby permit displacement of the mass by the hammer.

3. The combination of claim 2, further including:

means to bias the inertia mass to a seated position in which it isinitially engaged by the hammer; and

means to bias the automatic sear into engagement with the mass when thebolt assembly is displaced from the battery position.

4. In an automatic firearm:

a hammer mounted in the firearm for movement between recoil, cocked andfired positions, the cocked position being intermediate the recoil andfired positions;

a movably mounted inertia mass adapted to be engaged, displaced, andcleared by the hammer during movement between the recoil and cockedpositions;

an automatic sear bar mounted in the firearm for axial movement betweena first position in engagement with the mass and a second position inwhich the hammer may displace the mass, the first position being to therear of the second position; and

spring means to urge the sear bar rearwardly to the first position.

5. The combination of claim 4, further including:

a bolt assembly mounted in the firearm for movement between retractedand battery positions, the bolt assembly being contacted by the hammerin the fired position thereof; and

means on the bolt assembly to contact the automatic sear barintermediate the retracted and battery positions and to move theautomatic sear bar from the first position to the second position duringthe latter portion of bolt assembly movement from the retracted positionto the battery position.

6. The combination of claim 5, further including:

means to bias the inertia mass to a seated position in which it isinitially engaged by the hammer.

7. In a firearm adapted for automatic and semiautomatic operation, thecombination comprising:

a receiver section;

a bolt assembly mounted in the receiver section for reciprocatingmovement between retracted and battery positions;

a hammer mounted in the receiver section for pivoting movement betweenrecoil and fired positions, the hammer contacting the bolt assembly inthe fired position;

a sear mounted in the receiver section to engage and retain the hammerin a cocked position inter mediate the recoil and fired positions;

an inertia mass mounted in the receiver section for pivoting movementbetween a seated and displaced position such that falling movement ofthe hammer from the recoil position to the cocked position causes thehammer to engage and displace the inertia mass and to clear the inertiamass before reaching the cocked position and such that the hammerremains clear of the inertia mass in falling movement from the cookedposition to the fired position in both semiautomatic and automaticoperation;

means to return the inertia mass to the seated position after theinertia mass is cleared by the hammer during its falling movement;

an automatic sear mounted for movement in the receiver section between afirst position in which it engages the inertia mass in the seatedposition thereof and a second position in which the hammer may displacethe inertia mass; and

means to move the automatic sear from the first position to the secondposition as the bolt assembly moves into the battery position.

8. The combination of claim 7, wherein the inertia mass comprises:

a hub having a searing surface thereupon; and

wherein the automatic sear comprises:

a bar axially movable between the first and second positions and havinga surface which overlies and engages the searing surface of the hub whenthe bar is in the first position and slides out of contact with thesearing surface of the hub as the bar assumes the second position; and

means to move the bar from the second position to the first positionduring movement of the bolt assembly from the battery position to theretracted position.

9. The combination of claim 7, further including;

a selector in the receiver section for selecting either automatic orsemiautomatic operation; and a disconnect 1n the receiver section toengage the hammer and prevent its fall toward the fired position whenthe selector is positioned for semiautomatic operation and the hammerengaging sear is out of engaging contact with the hammer.

1. In a firearm adapted for semiautomatic and automatic operation, thecombination comprising: a hammer mounted in the firearm for fallingmovement between recoil and fired positions; a sear mounted in thefirearm to engage the hammer and retain it in a cocked positionintermediate the recoil and fired positions; and an inertia mass movablymounted in the firearm such that falling movement of the hammer from therecoil position to the cocked position causes the hammer to engage anddisplace the inertia mass and to clear the inertia mass before reachingthe cocked position in both semiautomatic and automatic operation andsuch that the hammer remains clear of the inertia mass in fallingmovement from the cocked position to the fired position in bothsemiautomatic and automatic operation.
 2. The combination of claim 1,further including: a bolt assembly mounted for reciprocating movementbetween retracted and battery positions in the firearm, the boltassembly being contacted by the hammer in the fired position thereof;and an automatic sear mounted in the firearm to engage the inertia masssuch that displacement of the mass by the hammer is prevented, theautomatic sear adapted to be contacted by the bolt assembly as it movesinto the battery position to remove the automatic sear from engagementwith the inertia mass and thereby permit displacement of the mass by thehammer.
 3. The combination of claim 2, further including: means to biasthe inertia mass to a seated position in which it is initially engagedby the hammer; and means to bias the automatic sear into engagement withthe mass when the bolt assembly is displaced from the battery position.4. In an automatic firearm: a hammer mounted in the firearm for movementbetween recoil, cocked and fired positions, the cocked position beingintermediate the recoil and fired positions; a movably mounted inertiamass adapted to be engaged, displaced, and cleared by the hammer duringmovement between the recoil and cocked positions; an automatic sear barmounted in the firearm for axial movement between a first position inengagement with the mass and a second position in which the hammer maydisplace the mass, the first position being to the rear of the secondposition; and spring means to urge the sear bar rearwardly to the firstposition.
 5. The combination of claim 4, further including: a boltassembly mounted in the firearm for movement between retracted andbattery positions, the bolt assembly being contacted by the hammer inthe fired position thereof; and means on the bolt assembly to contactthe automAtic sear bar intermediate the retracted and battery positionsand to move the automatic sear bar from the first position to the secondposition during the latter portion of bolt assembly movement from theretracted position to the battery position.
 6. The combination of claim5, further including: means to bias the inertia mass to a seatedposition in which it is initially engaged by the hammer.
 7. In a firearmadapted for automatic and semiautomatic operation, the combinationcomprising: a receiver section; a bolt assembly mounted in the receiversection for reciprocating movement between retracted and batterypositions; a hammer mounted in the receiver section for pivotingmovement between recoil and fired positions, the hammer contacting thebolt assembly in the fired position; a sear mounted in the receiversection to engage and retain the hammer in a cocked positionintermediate the recoil and fired positions; an inertia mass mounted inthe receiver section for pivoting movement between a seated anddisplaced position such that falling movement of the hammer from therecoil position to the cocked position causes the hammer to engage anddisplace the inertia mass and to clear the inertia mass before reachingthe cocked position and such that the hammer remains clear of theinertia mass in falling movement from the cocked position to the firedposition in both semiautomatic and automatic operation; means to returnthe inertia mass to the seated position after the inertia mass iscleared by the hammer during its falling movement; an automatic searmounted for movement in the receiver section between a first position inwhich it engages the inertia mass in the seated position thereof and asecond position in which the hammer may displace the inertia mass; andmeans to move the automatic sear from the first position to the secondposition as the bolt assembly moves into the battery position.
 8. Thecombination of claim 7, wherein the inertia mass comprises: a hub havinga searing surface thereupon; and wherein the automatic sear comprises: abar axially movable between the first and second positions and having asurface which overlies and engages the searing surface of the hub whenthe bar is in the first position and slides out of contact with thesearing surface of the hub as the bar assumes the second position; andmeans to move the bar from the second position to the first positionduring movement of the bolt assembly from the battery position to theretracted position.
 9. The combination of claim 7, further including; aselector in the receiver section for selecting either automatic orsemiautomatic operation; and a disconnect in the receiver section toengage the hammer and prevent its fall toward the fired position whenthe selector is positioned for semiautomatic operation and the hammerengaging sear is out of engaging contact with the hammer.